1. Field of the Invention
The invention relates to a fabric softening composition containing fluorescent whitening agents readily dispersible within the cationic surfactant phase and methods for their preparation and use.
2. The Prior Art
Liquid rinse cycle fabric softeners rehabilitate the softness of garments harshened during the washing process. Most commercially available fabric softeners use tallow based quaternary actives. They deposit onto the garments to provide a soft tactile feel. Unfortunately, quaternary actives also leave a yellowish cast on the fabrics. Laundry is left looking old and dingy. Science has learned to solve the problem. Whiteness/brightness can be restored through fluorescent whitening agents directly incorporated into the softening product.
Commercial whitening agents are complex organic molecules existing in either the acid or alkali metal salt form. Neither form can be conveniently incorporated into typical fabric softener systems. These systems have two phases--water and quaternary active phases. Salt forms of fabric whitening agents (FWA) are only moderately dispersible in the quaternary active phase. The salt forms dissociate in the fabric softener system. Dissociated electrolytes migrate into the water phase. As electrolyte content increases, the fabric softener system viscosity decreases. Watery products resulting therefrom are aesthetically unpleasing. Long term stability is also adversely affected.
When salt forms of the FWA are placed directly into the water phase, they are initially soluble. However, upon addition of quaternary actives to the system the salts separate from solution. Quaternaries lower the system's pH. The increased acidity is thought to cause the salt separation.
The FWA acid forms, though less dissociated, are not readily dispersible in quaternary actives. They are also not water soluble.
Neiditch et al, U.S. Pat. No. 3,904,533, describes a low electrolyte content liquid fabric softener emulsion containing fluorescent whitening agent. To achieve low electrolyte levels, Neiditch requires the use of at least two quaternary compounds. One of these compounds must be a low temperature stabilizing agent.
Simple solutions to the problems of dispersibility and stability of whitening agents in single active cationic systems has eluded researchers in the field till now.
It is an object of this invention to provide a low electrolyte content fabric softener system of satisfactory product viscosity and long term stability containing fluorescent whitening agents.
Another object of the present invention is to provide a method for dispersing fluorescent whitening agents in the quaternary active phase of fabric softener systems.